1. Field of the Invention
The present invention relates to an electrophotographic image forming apparatus which causes a developing unit to come close to or to be separated from a photoconductive drum unit in conjugation with the opening or closing operation of an upper frame, and, more particularly, to a gear power transfer mechanism for transmitting a rotating force of a drive motor to a side of the developing unit from a side of the photoconductive drum unit when the developing unit is caused to come close to the photoconductive drum unit.
2. Description of the Related Art
Image forming apparatus, such as laser printer or electronic copying machine are now widely used and these machines always require simplified operation procedures and stabilized printing quality.
Such image forming apparatus are structured so that an upper frame can be opened away from or closed toward a lower frame forming a boundary at an paper transfer path to reset a paper jam and to replace a developing unit and a photoconductive drum unit. Moreover, with such an opening or closing operation, the photoconductive drum unit provided within the upper frame is caused to come close to or to be separated from the developing unit and the power in the photoconductive drum unit is transferred to the developing unit via a power transmitting mechanism when the developing unit and photoconductive drum unit are caused to move close with each other.
FIG. 10A and FIG. 10B are structural diagrams schematically showing a typical example (Japanese unexamined patent Publication HEI 1-92776) of the image forming apparatus explained above.
This image forming apparatus divides the frame into an upper and a lower frame. The lower frame (hereinafter called a base) 1 is provided with a paper cassette setting part 11, a paper transfer path 12, a fixing unit 13 and a pick roller and a transfer roller (not illustrated). Meanwhile, the upper frame (hereinafter called a cover) 2 is provided with a photoconductive drum unit 3, a developing unit 4 and a link mechanism 5 and is rotatable around a rotating axis 14 relative to the base 1. At the dividing section of the base 1 and cover 2, a paper transfer path is formed.
Therefore, as shown in FIG. 10B, the cover 2 can be opened away from the base 1 at the boundary of the paper transfer path by rotation around the rotating axis 14.
The photoconductive drum unit 3 is fixed to the cover 2 and the developing unit 4 is swayably fixed to the cover 2. A mag roller (not illustrated) within a developing unit 41 can be moved closely to or separated from the photoconductive drum 31 through such swaying operation.
The link mechanism 5 sways the developing unit 4 in accordance with the closing and opening operation of cover 2, namely causes the developing unit 41 to come close to or separate from the photoconductive drum 31. For this purpose, the link mechanism 5 is composed of an L type rotatable arm 51, an L type transmitting arm 52 and a rotatable arm 53. The L type rotatable arm 51 has a guide hole 512 which engages with an engaging pin 511 provided on a base 1 at the one end thereof and rotates around the center axis 513 in accordance with the closing and opening operation of cover 2. The L type transmitting arm 52 couples the other end of the L type rotatable arm 51 and the one end of rotatable arm 53 to realize integrated operation of these arms. The rotatable arm 53 rotates around a rotating axis 531 and is provided, at the one end thereof, with a pushing mechanism 54 consisting of a plate spring to push the developing unit 4 toward the photoconductive drum unit 3.
Here, operations of link mechanism 5 will be explained.
First, the cover 2 shown in FIG. 10A is closed toward the base 1. In this case, the L type rotatable arm 51 of the link mechanism 5 is rotated around the rotating axis 513 simultaneously with depression in the direction of arrow mark A, thereby the transmitting arm 52 is pulled in the direction of arrow mark B and the rotatable arm 53 is driven to rotate counterclockwise around the rotating axis 531. Simultaneously, the pushing mechanism 54 integrated with the rotatable arm 53 is moved to the right side, pushing the developing unit 4 toward the photoconductive drum unit 3. As a result, the developing unit 41 and the photoconductive drum 31 are set in a closed condition. Since the developing unit 41 is provided with a pair of gap rollers 42 which are in contact with both end portions of an external circumference of the photoconductive drum 31, the magnetic roller and a photosensitive drum in the developing unit 41 are provided opposed with each other with a constant interval between them under such closed condition.
Next, the cover 2 shown in FIG. 10B is opened. Under this opened condition, the transmitting arm 52 of the link mechanism 2 is moved in the direction of arrow mark C and thereby a pushing force of the pushing mechanism 54 toward the developing unit 4 is eased. As a result, the developing unit 4 is separated from the photoconductive drum unit 3 with a recovery force of a spring (not illustrated) and, consequently, the photoconductive drum 31 is separated from the gap rollers 42.
Therefore, a large gap is generated, under this opened condition, between the developing unit 41 and the photoconductive drum 31 and, thereby a paper jam can be reset and replacement of the developing unit 41 and photoconductive drum 31 can be realized easily. Moreover, a surface of the photoconductive drum 31 can be protected from damage during the operations explained above.
As explained above, the image forming apparatus causes the developing unit 4 to come close to or to be separated from the photoconductive drum unit 3 in accordance with the opening and closing operations of the cover 2 and is also provided with a gear power transfer mechanism for transmitting the rotating force of a drive motor to a rotating part of developing unit 4 from the photoconductive drum unit 3 under the closed condition of these units explained above.
This gear power transfer mechanism 6 is composed, as shown in FIGS. 11A, 11B and FIG. 12, of a drive gear unit 62 coupled with the drive motor (not illustrated) on the side of photoconductive drum unit 3 and a driven gear unit 63 coupled with the rotating part of developing unit 41 (magnetic roller, developer agitating screw, etc.). The drive gear unit 62 is provided with three gears rotatably provided on a fixed substrate 61, namely a first intermediate gear 621 engaged with the drive motor, a second intermediate gear 622 always engaged with the first intermediate gear and a drive gear 623 always engaged with the second intermediate gear. The axis of first intermediate gear 621 is coupled with the drive mechanism of the photoconductive drum 31 and the second intermediate gear 622 is coupled with the rotating axis of a paper transfer roller (not illustrated).
On the other hand, the driven gear unit 63 is composed of a movable bracket 634 (hatched area in FIG. 12) provided movably in the direction of arrow mark to the fixed substrate 61 and three gears are rotatably provided on movable bracket 634. These three gears include a driven gear 631 engaging with the drive gear 623 on the side of photoconductive drum 31 when the developing unit 4 comes close to the photoconductive drum unit 3, a third intermediate gear 632 always engaging with the driven gear, and a fourth intermediate gear 633 always engaging with the third intermediate gear. The fourth intermediate gear 633 is provided with four pawls coupled with a coupling pawl gear on the side of developing unit 41 as shown in the figure. When these pawls couple, the magnetic roller and the developer agitating screw in the developing unit 41 are rotated. The gears explained above, although not limited thereto, may be manufactured through molding of the synthetic resin material.
Here, operations of this gear power transfer mechanism 6 will be explained.
First, the cover 2 shown in FIG. 11A is closed toward the base 1 and the developing unit 4 is moved toward the photoconductive drum unit 3. In this case, the driven gear 631 of the gear power transfer mechanism 6 engages with the drive gear 623 because both units are in the closed condition. As a result, a rotating force of the drive motor transmitted to the drive gear 623 through the first intermediate gear 621 and second intermediate gear 622 is further transferred sequentially to the driven gear 631, third intermediate gear 632 and fourth intermediate gear 633 from such drive gear 623 to rotate the magnetic roller within the developing unit 41. Therefore, the photoconductive drum 31 and developing unit 41 are driven by the single drive motor.
Next, the cover 2 shown in FIG. 11B is opened and thereby the developing unit 4 is separated from the photoconductive drum unit 3. In this case, the driven gear 631 of the gear power transfer mechanism 6 is separated from the drive gear 623 releasing the engagement and thereby the rotating force of drive motor is not transferred to the developing unit 41. Accordingly, the magnetic roller in the developing unit 41 is no longer rotated.
Meanwhile, in the image forming apparatus of the prior art explained above, the gap between the photoconductive drum 31 and developing unit 41 changes depending on a little deviation of a supporting axis of the gap rollers 42 and a rotating axis of photoconductive drum 31 which define such gap. Such change of gap has a large influence on the engagement between the drive gear 623 of the drive gear unit 62 and the driven gear 631 of driven gear unit 63. Namely, since positional relation between the drive gear unit 62 and driven gear unit 63 is determined with reference to the axis center of the gap rollers 42 of developing unit 4 and rotating center of the photoconductive drum 31. Even if the center positions are little deviated, adequate engagement between the drive gear 623 and driven gear 631 can no longer be attained.
Accordingly, here arises a problem wherein creak is generated between gears, for example, when engagement between the drive gear 623 and driven gear 631 becomes deep, or gear missing and gear skipping are generated when engagement becomes shallow, due to relative eccentricity of the rotating axes on the side of photoconductive drum unit 3 (rotating axes of the photoconductive drum 31 and drive gear) 623 and the driven axis axis on the side of developing unit 4 (supporting axis of gap rollers 42 and rotating axis of driven gear 631).
From such conditions, high level technique and longer processing time have been required for adjustment of the gap in order to attain adequate engagement between the drive gear 633 and driven gear 631. Thereby, the prior art has a disadvantage in that provision of gear power transfer mechanism 6 at the time of manufacturing the image forming apparatus and replacement of developing unit 4 and photoconductive drum 31 after manufacture of apparatus have been made ineffective. Therefore, it has also been difficult to prepare the gear power transfer mechanism 6 as a unit for maintenance work.